The present invention relates to an electronic device for converting a source of very low voltage into a voltage for operating electrical apparatus and to a self-contained detector-transmitter unit including such a device and to a unit comprising a self-contained detector-transmitter remote fire alarm.
The state of the art comprises a large number of devices which are sources of a very low electrical voltage. For example, thermocouples (when they are subject to a relatively low temperature differential of the order of 50.degree. to 100.degree. C.), microphones, certain electromechanical or electromagneto-mechanical pick-ups or probes, certain photoelectric cells. The voltages produced by these devices or pick-ups are generally used as input signals to control various electronic apparatus. These very low voltages are amply sufficient for such control since many forms of electrical apparatus are known which are capable of reacting to input voltages of around a few microvolts. These apparatus detect the very low voltages and are always provided with a source of electric power, a battery, power pack, mains connection for example. For certain applications in which very small supply voltages are quite adequate to operate the apparatus, the very low voltage devices or pick-ups themselves, which generally have very low internal impedances to give not inconsiderable current levels, would be capable of supplying the desired supply power, considered solely from the point of view of energy balance. This has been possible, at least under laboratory conditions, when the very low voltages are alternating voltages, such as is the case, for example, with an output signal from a microphone. On the other hand, when the very low voltage is a direct current voltage, such as produced, for example, by a thermocouple, the use of such a direct current voltage as a supply for operating an apparatus has not so far been possible in view of the very low voltage level.
Direct current voltage boosters are known which, for example, raise a direct current voltage of approx. 1.5 V from a battery to a level of 3 or 4.5 V. For such an arrangement to operate, however, it has so far always been necessary for the voltage which it is desired to increase, to be of a magnitude necessary to serve as a supply voltage for an electronic apparatus. This minimum supply voltage to operate an apparatus is around 1 V approximately, since the active elements suitable for use in electronic equipment of the type in question have threshold voltages which are close to 1 V. This prohibits operation when the supply voltage is much lower than 1 V. Consequently, sources of direct current voltage of a few mV (not exceeding 100 or 200 mV) have never been able to be used as an energy source capable of powering electrical apparatus, that is to say capable of making this apparatus independent of the presence of an independent power source (battery, power pack, mains, etc). These very low direct current voltage sources have therefore been used simply as a signal source and the apparatus which processed them have had to be provided with their own power source.
This is a very serious drawback when, in order to be able to be effectively used, the device or pickups supplying a very low direct current voltage, such as for example thermocouples serving as fire alarm detectors, have had to be installed in very large numbers, spread over a large space, at places often very inaccessible. Indeed, in such cases, considerable difficulties are found in inspecting, maintaining and, when necessary, exchanging batteries or power packs for providing energy to each of these devices or pick-ups.
In forest fire fighting for example, early detection of fires, the only way of effectively fighting large-scale fires, is possible only by means of providing detectors, typically thermocouples, in a very large number of places in the forest which is to be protected; no part of the forest should be more than about 20 to 30 m or even 50 m from a pick-up for detecting the start of a fire, for immediate detection of incipient fires to be ensured. In large forests which for example may extend over several tens of square kilometers, this requires the presence of thousands of detectors and the necessity for maintaining them, mainly due to the use of a battery, represents a tremendous increase in cost and organisational complexity, to the extent of rendering them virtually prohibitive.
The present invention sets out to provide an advantageous solution of the problems which have just been mentioned and its object is in particular to provide in a simple and advantageous manner an electronic device which makes it possible for a low voltage source to be used in a self-contained fashion.
Another object of the invention is to provide the necessary elements to allow use of this device in the production of a self-contained detector-emitter remote fire alarm unit.
Yet a further object of the invention being to provide a unit constituting a self-contained detector-emitter remote fire alarm which is of advantageous and simple construction while being at the same time capable of providing highly reliable technical service which may be expected of such a device, but at virtually insignificant running costs.